Fasting and growth hormone

Could fasting help build muscle and unleash anti-aging properties, via the release of human growth hormone?

The physiology of fasting is fascinating. The power of fasting lies not in the mere reduction of calories, but the beneficial hormonal changes. One of the main benefits comes from reducing insulin, but there are also increases in nor-adrenalin, cortisol, and growth hormone.

Collectively, these are known as the counter-regulatory hormones, since they all serve to increase blood glucose at a time that the body is not getting glucose from food. Here we focus on human growth hormone (HGH).

Human growth hormone

HGH is a hormone made by the pituitary gland (the master gland), which plays a huge role in the normal development of children and adolescents as the name implies. However, it also plays a role in adults. HGH deficiency in adults leads to higher levels of body fat, lower lean body mass (sarcopenia) and decreased bone mass (osteopenia).

Once released by the pituitary gland, HGH only lasts a few minutes in the bloodstream. It goes to the liver for metabolism, where it is converted into a number of other growth factors, the most important of which is Insulin-Like Growth Factor 1 (IGF1).

This is the same IGF1 that is connected to high insulin levels and many poor health outcomes, but remember, that this brief pulse of IGF1 from HGH lasts a few minutes at most. All hormones are secreted naturally in very brief bursts to prevent the development of resistance, which requires both high levels and persistence of those levels (this is indeed how insulin resistance develops).

Scientists first harvested HGH from cadavers in the 1950s (eeewww), but only synthesized it in labs in the early 1980s. Soon afterwards, it became a popular performance enhancing drug. Normal levels of HGH peak in puberty (as you might expect) and gradually decrease thereafter.

Growth hormone is typically secreted during sleep and is one of the so-called counter-regulatory hormones. HGH along with cortisol and adrenalin increases blood glucose by breaking down glycogen – so it counters the effect of insulin, hence its name. These hormones are typically secreted in a pulse just before waking (4 am or so) during the ‘counter-regulatory surge’. This is normal and is meant to get the body ready for the upcoming day by pushing some glucose out of storage and into the blood where it is available for energy.

When people say that you ‘must’ eat breakfast to have energy for the day, they are completely wrong. Your body has already given you a big shot of the good stuff and fueled you up for the day ahead. You don’t need to stuff your face full of sugary cereals and toast with jam to have energy. This is also the reason why hunger is lowest first thing in the morning (8 am) even though you have not eaten for 12 hours or so.

HGH for anti-aging and building muscle

HGH typically goes down with age and abnormally low levels may lead to lower muscle and bone mass. So, what are the effects of giving HGH in older people with very low levels? This was studied in 1990 in a New England Journal of Medicine article.

Group 1 is the HGH group and Group 2 is the control group (no HGH). Over 6 months, weight overall did not change between the two groups. But look at the lean body mass!

In a 2002 JAMA article, similar results were obtained in women as well. Sounds pretty great. So, why aren’t we using it for everybody? Well, there’s a little thing called side effects. Remember that this study only used it for people with very low HGH levels, not in people with normal levels.

There was an increase in blood sugars. This makes sense, since HGH is a counter-regulatory hormone. Pre-diabetes also significantly increased. There was an increase in fluid retention as well as blood pressure, too. Over the long term, there is also a theoretical risk of increased prostate cancer and heart problems (enlarged heart). So, that’s not very good news.

So artificial injections of HGH are out. What if there is an all-natural method of increasing growth hormone? What about, say, fasting?

Fasting to increase growth hormone

In 1982, Kerndt et al published a study of a single patient who decided to undergo a 40-day fast for religious purposes. Glucose goes down. From 96 initially, it drops to 56. Insulin goes way, way down. Starting at 13.5, it quickly drops to 2.91 and stays down. That is almost an 80% drop! If you are concerned about a disease such as type 2 diabetes, with hyperinsulinemia, nothing beats fasting to bring down those sky high insulin levels.

But our concern here is HGH. It starts at 0.73 and peaks at 9.86. That is a 1,250% increase in growth hormone. A shorter 5 day fast gives a 300% increase. All this HGH increases without drugs.

Other studies have shown the same increase in growth hormone. In 1988, Ho KY et al studied fasting and HGH. On the control day, you can see that meals (marked M) very effectively suppress HGH secretion. This is to be expected. Like cortisol, HGH increases glucose and thus is suppressed during feeding.

Fasting is a great stimulus to HGH secretion. During fasting, there is the spike in the early morning, but there is regular secretion throughout the day as well. Hartman et al also showed a 5 fold increase in HGH in response to a 2 day fast.

This HGH is crucial in the maintenance of lean mass – both muscle and bone. One of the major concerns about fasting is the loss of lean mass. Some people claim that fasting a single day causes loss of ¼ pound of muscle. Studies prove that this does not occur. In fact, the opposite can happen. In comparing caloric reduction diets to fasting, the fasting was 4 times better at preserving lean mass! Think about this for a second.

Let’s imagine that we are living in Paleolithic times. During the summer of plenty, we eat lots of food and store some of that as fat on our body. Now it is winter, and there is nothing to eat. What do you suppose our body does. Should we start burning our precious muscle while preserving our stored food (fat)? Doesn’t that sound pretty idiotic?

It’s as if you store firewood for a wood-burning oven. You pack lots of firewood away in your storage unit. In fact, you have so much, it is spilling out all over your house and you don’t even have enough room for all the wood you’ve stored. But when the time comes to start up the oven, you immediately chop up your sofa and throw that into the oven. Pretty stupid right? Why would we assume our body is also so stupid?

The logical thing to do is to start burning the stored wood. In the case of the body, we start to burn the stored food (fat stores) instead of burning precious muscle. Some protein is catabolized for gluconeogenesis, but the increase in HGH maintains lean mass during fasting.

Implications for athletes

This has enormous implications for athletes. This is called ‘training in the fasted state’. Increased nor-adrenalin from fasting will pump you up to train harder. At the same time, the elevated HGH stimulated by fasting should increase muscle mass and make recovery from a workout easier and faster. This would be an important advantage in elite level athletes, and we are seeing more and more interest in doing this exact sort of protocol.

It is not by accident that many of the early proponents of training in the fasted state are bodybuilders. This is a sport that demands, in particular, high intensity training and extremely low body fat for definition.

For example, Brad Pilon, who wrote the book “Eat, Stop, Eat” is a bodybuilder, as is Martin Berkhan, who popularized the ‘lean gains’ method of fasting. Somehow, I don’t think that fasting for these two fellows was ‘eating’ their muscle.

So, for all those people who thought that fasting would make you tired, or that you could not exercise during fasting, well, you’re just wrong. Fasting does not ‘burn’ muscle. There is no ‘starvation’ mode from fasting where you shrivel up into the fetal position on your couch.

Rather, fasting has the potential to unleash the anti-aging properties of HGH without any of the problems of excessive HGH (prostate cancer, increased blood sugar, increased blood pressure). For those interested in athletic performance, the benefits are even greater.

So, let’s see. Train harder. Lose weight. Faster recovery. Decrease insulin and insulin resistance. Decrease blood sugars. All of these benefits are achieved without drugs, supplements or cost. Yes, like all the best things in life, it’s free. So why is everybody so against it?

Wonderful article on fasting!. Dr. Fung, you are on a great roll against the unbelievable destruction by the modern scourge of Type II diabetes and the other likely related and similarly caused diseases of modern civilization, i.e., obesity, cancer, osteoporosis, Alzheimers, many neurological and behavior diseases, etc. I nominate you and Gary Taubes for the Nobel prize in medicine. Keep it up for the world is bound to eventually wake up and see that what you are saying is obvious. There are of course others saying the same thing, but you are doing it in a way that people can understand and you pull no punches toward and seem to have no fear of the deeply corrupt, nutritionally ignorant and misguided drug pushing for every problem medical establishment. God speed to you Dr. Fung and thank you for what you do.

I have been fasting daily for the whole month of October in and effort to drop body Fat. I normally do 18-6 window,, my results were a 3.5% loss of BF I was amazed at these results and very satisfied . When not fasting I eat a LC diet , drink tons of water . I work out daily doing HIIT or Lifting and walking in a fasted state .. always . I sleep like a rock,, my hair grows at a rapid pace , my energy level is the best its ever been, My moods are always positive . And ZI love the lifestyle of IF. I read Dr. Fung's articles as soon as they hit the website . I love the IF lifestyle and promote it to everyone who will listen. Thank You Dr. Fung for all your research and information you provide on this subject,, it has changed my life for sure . Please do not stop informing us

Very informative article! I'm wondering how well very low calroic intake affects HGH compared to complete fasting? For example what if I just drank wheatgrass juice in the morning. Is that considerable enough to breaking my fast?

Thank you so much for the article. I am really into this topic and also do intermittent fasting every day, eat huge amounts of veggies and no meat, dairy and gluten. So when we are on a fast our human growth hormone increases a lot because we lack glucose. HGH is known for its anti aging and anti inflammatory properties and also protects our muscles and proteins. I also feel much better when skipping breakfast and doing my work out in a fasted state... But on the other hand IGF 1 (insulin like growth factor) is produced out of HGH in the liver. IGF1 really promotes cell growth and is linked to cancer... So here is what confuses me a lot! I do not understand why so many doctors and researchers reccomend high levels of HGH for anti aging and anti cancer and stuff, but on the other hand low levels of IGF1. Is this even possible?? For me it is clear that fasting is healthy because our body does not need to put energy in metabolism and also less free radicals are produced and insulin and blood glucose is low.. But my major concern is IGF1.. It would be so great if you explained this in a scientific way.
Thank you so so much!

The key to minimized aging is a healthy balance of HGH/IGF1. Both extremes are harmful: low levels result in a generally weak body, and high levels result in increased risk for overgrowth (ie cancer) and increased wear of physiological/metabolic pathways.

I did a 30-day water only fast at a water fasting resort, and I lost so much muscle and overall weight. I was thinner but very flabby and with loose skin. I was also extremely exhausted and slept a lot. Headaches, constipation, and insomnia (waking up at night) were a daily experience. How can you say you don't lose muscle mass on an extended fast? That's just not true. Everyone at the resort experienced the same as I did. When I got home after the month I had to start working out again because everything, and especially my butt, was sagging, with absolutely no muscle tone. My family said I looked thinner but unhealthy. Please explain how you think muscle mass is maintained on a water fast. And you can't work out while on a fast, with no food intake. Your cortisol would spike and your adrenals would be exhausted... Besides being too exhausted to workout to begin with.

I started fasting, well this is week 5. I chose to do 5/2 - 24 hours broken with a normal meal. I wanted to tap the benefits of increased growth hormone and also getting my insulin down. I knew it would take a while as I was pre-diabetic. Week 4 I felt the difference. I have lost 10 lbs. I have a scale that does body composition. My lean mass has gone up just a bit and my body fat % has gone down by 3.5%. I'm stoked. I have the metabolic syndrome and struggled because I am fodmap sensitive. I was doing low glycemic index a few years ago and did great, then fodmap killed me. I gained back all the weight. Now I have found some slowly digestible carbs I can eat, and some veges too. I am trying to minimize carbs though, doing the high fat/protein as best I can. I exercise every day already, and am back to weight lifting. I have lost about 20 inches, 3 from my waist!

I started keto 18 months ago. In the first 9 months, I lost 17 kilos (from 95 to 78) and my fat percentage dropped from 30% to 22%. Without any change in diet, the process stopped for 5 months. Then I started fasting. Since then my weight oscillates -6kg (down to 72) during fasting and then +6 kg back. My weight is stagnating since then and my fat content is back at 24%. My BMI is still 26. Something is horribly wrong. My body composition keeps worsening, my weight is stagnating on keto + intermittent + 8 day long fastings. My keto tests are always excellent! Suggestions?

Hi Kate,
I am curious if you would share what your daily/weekly/ monthly meals and fasting schedule look like. We are already somewhat vegetarian except that we do eat eggs, cheese and seafood - my husband eats almost no dairy but we have it mostly for our children. I would like to move away from animal proteins and we need to try gluten free. Do you have children? If so, do they participate in an intermittent fasting schedule too? Thank you in advance if you are able to share!

There is a study I hear shows a 2000% increase in growth hormone in men and 1300% increase in women after 24 hour fast. 2000% is 20 fold increase. Might it be that it rises rapidly to 2000%, then decreases and starts to rise throughout the fast? Or might it be different measuring methodologies?

In your article you state that:
"Some people claim that fasting a single day causes loss of ¼ pound of muscle. Studies prove that this does not occur."

However, looking at the study you yourself provided, the numbers state very clearly that while fat loss was the same in the caloric restriction (CR) group vs. the alternative day fasting group (ADF), the ADF group lost more lean mass. This does not support your claim and if anything, it disproves it.

Michael, Dr Fung and Zoe Harcome have explained this before. The human body is not a steam engine/toaster oven....so normal rules of number crunching don't apply. I.e. 4-2 does not always =2 when hormones get involved. I think with autophagy, the body is doing some tricky stuff that science will always struggle to explain....like breaking down the junk and building up the good stuff. The reports of People who are doing this do not match the hard data crunching. As post menopausal women in our 60's, my gym buddy and I have got stronger, healthier, more robust using Dr Fungs and other advice we find on this site. This is unheard of in the normal world. Our strategies have evolved and now we have settled mostly on one or two mealS a day. So we don't really care about your sums adding up. Go Jason!!

Thank you for your reply. I believe that I can help you with explaining how and why this works. The reason is simple: exercise. Exercise makes all the difference between losing or gaining lean mass. The studies that were presented in this article, as far as I have understood it, were not conducted with athletes, but with average people who wanted to lose weight. This is why the numbers look like they do.

Still, the point remains that the studies presented here showed that the claim that the author was trying to revoke was actually true. That was what I wanted to point out.

Furthermore, even though the human body is not a toaster, rules of number crunching absolutely do apply in the long term. Even if variations are seen in the short term (think days) calories/nutrients in vs. calories/nutrients out still matters a lot in the long term (think weeks) and can be supported by relatively simple maths. Of course, this is assuming a healthy body with an intact hormonal balance.

I'm just starting so please forgive me if I missed something in the books. I'm wondering when you say fasting daily for a month, is that the 24 hour fast or 20 hour fast? I cant seem to make it the 24 hours without feeling sick. I'm eating 2 small Keto meals (in 4 hours ) on weekdays and doing the 16-8 fast on weekends. I am only walking but hoping to continue lifting weights soon. I had a back injury that took me out and I gained weight. UGH. Anything you can tell me to jump start my weight loss? Can I have a few drinks on the weekend or will it slow me down? Thanks for your help.

I agree with you, Muslims do that in Ramadan month for all of the month and they became healthier and build a very gentle bodies. Also, they are fasting Monday and Thursday from every week as "Sunna orNaffella".Acutally, It is the greatest religion.
I am Muslim and very happy for that.
And YOU?

I go to university at 10 am ...and coming back home at 6 pm around =almost8/ 9 hours without eating any foods ,some biscuits + water etc. Sometimes ......I am lean and wanna grow muscle like any body builder ...work out 4 /5 days in a week .....
Am I right about my plans ???please send me in a mail .

I go to university at 10 am ...and coming back home at 6 pm around =almost8/ 9 hours without eating any foods ,some biscuits + water etc. Sometimes ......I am lean and wanna grow muscle like any body builder ...work out 4 /5 days in a week .....
Am I right about my plans ???please send me in a mail .